Conventional content control systems that deliver contents through networks respectively have employed such techniques as the DRM (Digital Rights Management), digital watermarking, and user authorization. The DRM technique aims at protecting the copy rights of pay digital contents, etc. and is used to restrict copying of audio and video content files delivered from servers to user terminals, respectively.
The watermarking technique is used mainly for two purposes; one is to insist the copyrights of contents and the other is to identify illegal users of contents. For the former, the copyright owner ID is buried in each of those contents. For the latter, the user ID of each content is buried in the content. Particularly, the latter technique employs the following two cases; in one case, terminals bury such watermarks and in the other case, servers bury such watermarks. For example, JP-A No. 2007-207051 discloses one of the latter cases; the servers bury such watermarks.
The user authorization technique authorizes each user with use of the user ID, password, etc. Each server can control the delivery of contents according to the result of such authorization.